An environmental group known for confronting whaling ships at sea asked the Supreme Court today to lift an injunction barring it from maneuvers that harass Japanese whalers.

The Sea Shepherd Conservation Society filed an appeal of a 9th U.S. Circuit Court of Appeals order in December requiring the nonprofit to stay at least 500 feet away from Japanese whaling ships.

Charles Moore, the attorney representing Sea Shepherd, said at a National Press Club briefing that the San Francisco-based 9th Circuit's three-sentence injunction surprised the group because it was issued without warning or a chance to argue in front of the judges and without being requested by Japan's Institute for Cetacean Research.

The court issued the preliminary injunction sua sponte, or "of its own accord."

Moore described the move as "highly unusual," while Robert Kennedy Jr., participating by phone, called it "very, very dubious and strange and unique."

"I've never seen a species of injunction like this before in my 30 years as a practicing attorney and litigator," said Kennedy, who is a senior attorney for the Natural Resources Defense Council and president of Waterkeeper Alliance.

The injunction overturned a March 2012 ruling from U.S. District Judge Richard Jones in Seattle, who denied the institute's initial request for an injunction on the grounds that it would not succeed in trial. Sea Shepherd's tactics are low-level harassment, and the institute does not face irreparable harm if the group continues its campaign, Jones ruled. He added that if the case were to proceed, the institute would come to the courtroom with "unclean hands."

The institute is whaling in the Australian Whale Sanctuary, despite an injunction from the Australian courts, Moore said.

Whaling was outlawed worldwide in 1986, but Japan continues to hunt whales under a research exemption in the Southern Ocean Whale Sanctuary and surrounding waters. An estimated 20,000 whales have been killed for research by Japan, without a single peer-reviewed article being published in a scientific journal, Kennedy said.

"They are really a pirate organization masquerading as a science research group," he said.

The international and scientific communities broadly oppose whaling for research, he said. The U.S. State Department also opposes whaling.

Scott West, an investigations operative for Sea Shepherd, noted that the injunction applies only to Sea Shepherd Conservation Society U.S. and its founder, Paul Watson. Other nations' Sea Shepherd groups are separate entities, he said.

The injunction has prevented the United States from participating in the annual campaign to stop whaling in the Southern Ocean, which typically involves positioning watercraft to block ships from hauling whale carcasses on board, throwing a vomit-smelling concoction called "stinky butter" on board, or snagging ship propellers.

Four vessels flying Australian and Netherlands flags are currently patrolling the Southern Ocean, West said.

"All of these entities have picked up the mission," West said. "Sea Shepherd U.S. is complying with, albeit ridiculous, the injunction. ... We're not going to be in violation of federal law."

The whaling season typically is between December and March, during the Antarctic summer. No whales have been killed this season so far, said Susan Hartland, Sea Shepherd's administrative director.